1. Field of the Invention
This invention relates to a digitizer to provide a digital representation of phase angle, given sine and cosine analog inputs. More particularly, this invention relates to a digitizer for use with capacitive encoders that are amplitude demodulated. Variations in the gap spacing between capacitor plates in such encoders affect the amplitudes of the sine and cosine signals generated by the encoder, although the relative sine and cosine maximum signal amplitudes remain equal to each other. The present invention is designed to eliminate problems caused by such amplitude variations.
2. Description of the Prior Art
Circuitry for providing a digital angle representation as a function of analog sine and cosine inputs is disclosed in U.S. Pat. Nos. 3,624,636 to Diederich, 3,504,361 to Catton and 3,636,544 to Farneth. A digitizer employing sine and cosine analog inputs is also disclosed in EDN, February 1967, volume 12 No. 3, page 67, "Degrees to Cycles to Decimals" by Shatavsky, as well as in U.K. Patent No. 1,201,118 to O'Brien. These publications disclose various methods for the generation of a digital angle signal as a function of sine and cosine analog inputs.